1. Field of the Invention
The invention relates to a touch panel, and particularly to a system and method for motion detection.
2. Description of the Related Art
Generally, each human body has different equivalent capacitance value to the ground. Therefore, when a human's finger is touching a key or a metal pad disposed on a touch panel, the effective capacitance value of the metal pad touched by the finger varies. Even though the human's body does not contact the touch panel, some parasitic capacitance is still generated inside the touch panel circuit. Many conventional touch panels utilize the feature of the above-mentioned capacitive effect to determine if a human's body gets close to or even touches a key or a metal pad on the touch panel according to the number of charge and discharge cycles of the stray capacitors.
FIG. 1 illustrates a schematic diagram of a conventional motion detection system. FIG. 2 illustrates a flow chart of a conventional motion detection method.
Referring to FIG. 1, the conventional motion detection system 100 includes a timing controller 120, a plurality of metal pads 101˜1ON (where N>1 and N is a positive integer), a counter 130, a plurality of switches 151˜15N, and a control unit 140. The timing controller 120 generates a plurality of control signals to the switches 151˜15N for controlling the switching positions. On condition that nobody touches those metal pads, the switch related to one of the metal pads (such as the metal pad 101) is first connected to a high voltage Vcc and the switches 152˜15N related to the other metal pads 10n (where n is a positive integer and 2≦n≦N) are grounded. At this moment, the parasitic capacitor C12 exists between the metal pad 101 and the metal pad 102 and is charged by the high voltage Vcc. Next, the switch 151 (or the metal pad 101) is floated so that the parasitic capacitor C12 discharges through a corresponding resistor R (not shown). During a predetermined period T, the above-mentioned steps are repeated until the average number Mref of the charge and discharge cycles is recorded. On the other hand, if a human's finger is touching or close to the metal pad 101, parasitic capacitors C1˜CN with different capacitance values are generated between the metal pad 101 and the other metal pads so as to change the effective capacitance value of the metal pad 101, finally influencing the number of the charge and discharge cycles of the metal pad 101. Wherein, the voltage Vb is a ground voltage that the human body touches.
Referring to FIG. 2, the conventional motion detection method comprises the steps as follows. First, in step S201, the average number Mref of the charge and discharge cycles is calculated and then recorded during the predetermined period T if it is assured that nobody touches the metal pads. Then, in step S202, the number of the charge and discharge cycles for each metal pad is likewise calculated during the predetermined period T on condition that it is unknown whether anybody is touching the metal pads. Subsequently, in step S203, the numbers M1˜MN of the charge and discharge cycles for the metal pads are respectively compared with the average number Mref in order to determine respectively if the differences between the numbers M1˜MN and the average number Mref are large enough to indicate that somebody is touching or close to the metal pads. If it is assured that somebody is touching one of the metal pads, the system will perform the related processing in step S204. If not, the flow returns to the step S202.
However, with respect to the conventional motion detection technique, the effective capacitance values (or capacitive effect) are significantly interfered by either external noises or external environmental factors while detecting. Meanwhile, due to the different effective capacitance value for each individual and incapable of making real-time dynamic calibration, the traditional motion detection technique causes the problems of unsatisfactory accuracy and high correlation between individuals.